Here is my query?

UPDATE users 
SET reputation = reputation - (CASE WHEN id = 29 THEN 2 
                                    WHEN id = 30 AND NOT 0 THEN 15
                                    ELSE 0 
WHERE id IN (30, 29);

Sometimes it throws this error:

#1690 - BIGINT UNSIGNED value is out of range in '(spy.users.reputation - (case when (spy.users.id = 29) then 2 when ((spy.users.id = 30) and (not(0))) then 15 else 0 end))'

As you see in the error message, reputation column is UNSIGNED, and I need to keep it 1 at least .. something exactly like stackoverflow: if a user has 1 rep and he gets a downvote, his rep will still remain 1. Well how can I fix that update query to prevent failing in such a case?

Noted that using greatest(): doesn't make any different. I mean this won't work either:

UPDATE users 
    SET reputation = GREATEST(reputation -
                               (CASE WHEN id = 29 THEN 2 WHEN id = 30 AND NOT 0 THEN 15
                                     ELSE 0 END), 0)
WHERE id IN (30, 29);
  • 1
    NOT 0 is always "true"; why is that part of the expression?
    – Rick James
    Commented Aug 2, 2016 at 0:32
  • @RickJames Please take a look at this.
    – stack
    Commented Aug 2, 2016 at 8:12

2 Answers 2

SET reputation = 
        CAST(reputation AS SIGNED) - ( ... )
  • Could you please elaborate? Commented Aug 2, 2016 at 8:10
  • @dezso - The CAST treats reputation as a signed INT, thereby avoiding the error message. The GREATEST says "take 1 or that other expression, whichever is larger". This prevents actually trying to store a negative number in the UNSIGNED reputation. The 1 comes form the OP's requirements. (Other answers read that as 0.)
    – Rick James
    Commented Aug 2, 2016 at 16:41

[Based on Rick Jame's answer, but expands to include original question and explains the meaning]

Take the GREATEST clause and wrap it within a CAST to return it back to an unsigned type before it is used to update the field.

The 1 represents the greatest is the lowest value that can be stored in the reputation field, and is the number you can modify if you want to set a minimum value.

UPDATE users 
SET reputation = CAST(
        (reputation - (
                WHEN id = 29 THEN 2
                WHEN id = 30 AND TRUE/FALSE THEN 15
                ELSE 0
WHERE id IN (30, 29)

The TRUE/FALSE piece is where the PHP script can inject the correct true or false value instead of the mySQL engine evaluating a boolean expression each time it executs.

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